Since the mid 1990s one of the most rapidly growing retail sectors is referred to as electronic commerce. Electronic commerce involves the use of the Internet and proprietary networks to facilitate business-to-business, consumer, and auction sales of everything imaginable, from computers and electronics to books, recordings, automobiles, and real estate. In such an environment consumer privacy is becoming a major concern.
However, the mere fact that electronic commerce is conducted over an existing open network infrastructure such as the Internet runs counter to the privacy of the consumer. Often, there are legitimate reasons for a party to remain anonymous towards peers and outsiders.
As the collection and exploitation of private information become more of a concern, users are less willing to give out information, and may want to conduct transactions under a pseudonym or anonymously. A user in such a pseudonymous or anonymous transaction may want a receipt of the transaction (e.g., receipt of a payment), which can be used at a later point in time. For example, the user may receive a receipt for a payment giving him access to certain information on the World Wide Web and the Internet, and may want to use that receipt at (a) later point(s) in time to get the information or to prove that a particular transaction took place, e.g., that the user made a payment. In a pseudonymous or anonymous system, where the user is making the transaction anonymously or under a pseudonym P, a ‘classical’ digital receipt (e.g., a digital signature) would prove the pseudonym's P involvement in the transaction. However, such a receipt may be intercepted and used by anyone claiming to be the pseudonym P. Also, the user acting under pseudonym P may give the receipt away to his friends, enabling those friends to access the same information.
There is a call for a method where a user in a pseudonymous or anonymous system is able to prove to be the legitimate owner of a transaction receipt, without revealing his/her real identity. In the course of this the user should be prevented from giving away his receipts to other parties, e.g., to his/her friends.